The present invention relates to a thermoplastic elastomer composition, more particularly relates to a thermoplastic elastomer composition excellent in durability and excellent in resultant tire inside appearance and air permeation preventive property and to a pneumatic tire and hose using the same. The present invention further relates to a process for producing a thermoplastic elastomer composition, more particularly a process for producing a thermoplastic elastomer composition capable of providing a domain rubber having a reduced particle size with a material having a high rubber ratio and a process for producing a pneumatic tire using the same.
Compositions having a low gas permeation performance (gas barrier performance) composed of thermoplastic resin/thermoplastic resin-based blends such as a high density polyethylene resin and nylon 6 or nylon 66 (HDPE/PA6.66), a polyethylene terephthalate and aromatic nylon (PET/MXD6), a polyethylene terephthalate and vinyl alcohol-ethylene copolymer (PET/EVOH), where one thermoplastic resin is layered over the other layer to form plural layers by molding, and processes for producing the same, are already known from Isao Hata: Kobunshi (Polymers), 40 (4), p. 244 (1991) etc. Further, an application regarding the use of such a composition as the inner layer of a tire has been already filed by the present assignee (Japanese Patent Application No. 7-55929). However, since these materials are thermoplastic resin/thermoplastic resin blends, while they are superior in gas barrier property, they lack flexibility, and therefore, such films are liable to break when the tire is in running.
Further, there are also examples of use of a thermoplastic elastomer composed of a rubber and a thermoplastic resin for the inner liner or a tire (Japanese Patent Application No. 8-183683), but in general a flexible material superior in durability has a low heat resistance. With a thermoplastic elastomer using a thermoplastic resin having a melting point less than the tire vulcanization temperature as a matrix, when the vulcanization bladder is released at the end of the vulcanization of the tire, the tire inside surface is liable to become poor in appearance due to the thermoplastic resin sticking to the bladder, rubbing with the bladder, etc.
Research directed to the difference in viscosities at the time of processing in mixing of rubbers and resins has been known in the past. Among these, the capability of reducing the domain dispersion particle size the most in the state where the ratio of melt viscosities of the rubber/resin is brought close to 1 (that is, no difference in viscosities) has been reported in S. Wu, Polym. Eng. Sci., 27(5), 1987. If using these technologies to fabricate a thermoplastic elastomer having more flexibility, larger strength and elongation, and superior durability by raising the rubber ratio, while keeping the ratio of melt viscosities of the rubber/resin at 1, the rubber becomes the matrix and thermoplasticity is no longer exhibited.
In a laminate in which dynamic fatigue resistance is required such as tire, hose, when using a gas permeation preventive thermoplastic elastomer composition composed of rubber/resin dispersed therein, it is known to obtain a balance between the flexibility and gas permeation preventive property by making joint use of a flexible N11- or N12-nylon and superior gas permeation preventive property N6- or N66-nylon. Further, the present inventors have proposed to define the volume fraction and melt viscosity using the equation of xcex1:
(xcfx86d/xcfx86m)xc3x97(xcex7m/xcex7d) less than 1.0
wherein the volume fractions of the continuous phase component and dispersion phase component in the thermoplastic elastomer composition are xcfx86m and xcfx86d and the melt viscosities of the components are xcex7m and xcex7d and further to bring the ratio of viscosities xcex7m/xcex7d close to 1 to reduce the rubber dispersed particle size of the domain to improve the durability (Japanese Patent Application No. 8-193545, Japanese Patent Application No. 9-175150, and Japanese Patent Application No. 10-235386). However, the durability at low temperatures was insufficient by just reducing the rubber particle size.
An object of the present invention is to solve the above-mentioned problems and to provide a thermoplastic elastomer composition which is excellent in heat resistance and durability, while maintaining the flexibility and to provide the use of the elastomer composition for the air permeation preventive layer of a tire so that, when the elastomer composition is used as the air permeation preventive layer of a tire, it gives a tire excellent in heat resistance and durability, while being excellent in flexibility and, further, does not stick on the shaping bladder and, therefore, is excellent in surface finish as well.
Another object of the present invention is to provide a process for producing a thermoplastic elastomer composition which is free from reversal of the dispersed structure of the resin component as the continuous phase (matrix) and the rubber component as the dispersion phase (domain) even when the rubber ratio is 50% or more and, further, has the properties of being more flexible, large in strength and elongation as well, and superior in durability.
A still further object of the present invention is to provide a thermoplastic elastomer composition having a structure having a blended resin as a matrix and a rubber elastomer dispersed therein, wherein not only the dispersed particle size of the rubber elastomer, but also the structure of the blended resin of the matrix phase are controlled to improve the durability, in particular the durability at low temperatures, while maintaining the air permeation preventive property and a pneumatic tire and hose using that thermoplastic elastomer composition.
In accordance with the present invention, there is provided a thermoplastic elastomer composition comprising an elastomer component containing a nylon resin having a melting point of 170 to 230xc2x0 C. and a halide of an isobutylene-p-methylstyrene copolymer, which is dynamically vulcanized to a gelation rate of 50 to 95%.
In accordance with the present invention, there is provided a thermoplastic elastomer composition characterized in that the nylon resin is composed of nylon 11 or nylon 12 and nylon 6/66 copolymer at a ratio of 10/90 to 90/10, in that a molecular weight distribution (Mw/Mn) of a blend of the nylon 11 or nylon 12 and the nylon 6/66 copolymer in the thermoplastic elastomer composition is Mw/Mn less than 10.0, preferably Mw/Mn less than 5.0, and in that a cross-linking agent for cross-linking the elastomer component is previously mixed into the elastomer component in advance.
In accordance with the present invention, there is provided a pneumatic tire having the above thermoplastic elastomer composition as an air permeation preventive layer.
In accordance with the present invention, there is further provided a process for producing a thermoplastic elastomer composition comprising the steps of mixing a rubber composition (A) and a thermoplastic resin (B) under conditions of the following equations (I) and (II):
(xcfx86A/xcfx86B)xc3x97(xcex7B/xcex7A) less than 1.0xe2x80x83xe2x80x83(I)
0.8 less than (xcex7A/xcex7B) less than 1.2xe2x80x83xe2x80x83(II)
wherein xcfx86A: volume fraction of rubber composition (A), xcfx86B: volume fraction of resin (B), xcex7A: melt viscosity of rubber composition (A), xcex7B: melt viscosity of resin (B)); and
mixing the resultant composition (C) and a rubber composition (D) under conditions of the following formulas (III) and (IV):
(xcfx86D/xcfx86C)xc3x97(xcex7C/xcex7D) less than 1.0xe2x80x83xe2x80x83(III)
0.8 less than (xcex7C/xcex7D) less than 1.2xe2x80x83xe2x80x83(IV)
wherein xcfx86D: volume fraction of rubber composition (D), xcfx86C: volume fraction of composition (C), xcex7D: melt viscosity of rubber composition (D), xcex7C: melt viscosity of composition (C).
In accordance with the present invention, there is provided a pneumatic tire using a thermoplastic elastomer composition prepared by the above process of production for an air permeation preventive layer of the tire.
In accordance with the present invention, there is further provided a thermoplastic elastomer composition comprising an elastomer composition (Axe2x80x2), as a dispersion phase, and a thermoplastic resin composition (Bxe2x80x2), as a matrix and having said thermoplastic resin composition composed of a blend of at least two thermoplastic resins, wherein the dispersed particle size of the elastomer composition (Axe2x80x2) is not more than 10 xcexcm and the particle size of a resin composition (Dxe2x80x2) dispersed in a matrix resin composition (Cxe2x80x2) in the thermoplastic resin composition (Bxe2x80x2) is smaller than the particle size of the dispersed rubber.
In accordance with the present invention, there is further provided a thermoplastic elastomer composition, wherein the elastomer composition (Axe2x80x2) and the thermoplastic resin composition (Bxe2x80x2) satisfy the following equations (V) and (VI):
(xcfx86d/xcfx86m)xc3x97(xcex7m/xcex7d) less than 1.0xe2x80x83xe2x80x83(V)
0.8 less than (xcex7m/xcex7d) less than 1.2xe2x80x83xe2x80x83(VI)
wherein xcfx86d: volume fraction of elastomer composition (Axe2x80x2), xcfx86m: volume fraction of thermoplastic resin composition (Bxe2x80x2), xcex7d: melt viscosity of elastomer composition (Axe2x80x2), xcex7m: melt viscosity of thermoplastic resin composition (Bxe2x80x2) and
the matrix resin composition (Cxe2x80x2) and dispersed resin composition (Dxe2x80x2) in the thermoplastic resin composition (Bxe2x80x2) satisfy the following equations (VII) and (VIII):
(xcfx86Dxe2x80x2/xcfx86Cxe2x80x2)xc3x97(xcex7Cxe2x80x2/xcex7Dxe2x80x2) less than 1.0xe2x80x83xe2x80x83(VII)
0.8 less than (xcex7Cxe2x80x2/xcex7Dxe2x80x2) less than 1.2xe2x80x83xe2x80x83(VIII)
wherein xcfx86Dxe2x80x2: volume fraction of dispersed resin composition (Dxe2x80x2), xcfx86Cxe2x80x2: volume fraction of matrix resin composition (Cxe2x80x2), xcex7Dxe2x80x2: melt viscosity of dispersed resin composition (Dxe2x80x2), xcex7Cxe2x80x2: melt viscosity of matrix resin composition (Cxe2x80x2).
Further, in accordance with the present invention, there is a provided a thermoplastic elastomer composition characterized in that a blend of at least two polyamide resins is selected as the thermoplastic resin composition (Bxe2x80x2) and in that a polyamide resin having at least seven methylene groups with respect to one amide group is contained as the matrix resin composition (Cxe2x80x2) in the thermoplastic resin composition (Bxe2x80x2) and a polyamide resin having less than seven methylene groups with respect to one amide group is contained as the dispersed resin composition (Dxe2x80x2).
Further, in accordance with the present invention, there is provided a pneumatic tire and hose using the thermoplastic elastomer composition obtained according to the present invention.